This invention relates to a fluid actuated operator for raising and lowering an overhead door. A typical use of the new door operator and the control system therefor is in connection with overhead garage doors of the multiple panel or single panel types.
Most overhead doors are counterpoised with a spring or a counterweight system so that energy will be stored during door closing and energy may be extracted during door opening. If the door is counterpoised as well as possible, the amount of manual energy required for opening the door need be only sufficient to make up the frictional and other losses in the system. During opening most of the energy for lifting the door is derived from that which is stored in the spring or counterweight system. Also, during door closing, only an amount of energy is required for making up the frictional losses since most of the energy that is transferred to the spring or counterweight storage system is derived from the weight of the descending door.
Use of electromechanical operators for automatic opening and closing of overhead doors is becoming quite common, especially in connection with folding overhead doors that are used on garages associated with homes. When these electromechanical door operators are used on newly constructed doors or retrofitted to existing doors, the spring or counterweight counterpoising system enables a smaller drive motor to be used since, as with a manually operated door, energy only needs to be put into the system for overcoming losses in the mechanism since the door opens largely under the influence of the counterpoising system and closes largely under the influence of its own weight.
Doors which have stored energy devices such as those described above can create a number of problems for the user. For instance, if the user or other inexperienced person or, even an experienced person, attempts to adjust the amount of counterweight or the torque of the spring to obtain good balance or counterpoising, releasing the spring or counterweight for adjustment may result in a sudden release of all of the stored energy. Breakage of a link or cable, or the like, could have similar results. This could propel a tool which a person is using to make the adjustment through the air and possibly cause injury or some part of the counterpoising mechanism may be set in high speed motion which might cause injury if the person is in contact with the part. For these and other reasons, eliminating the energy storage devices would be desirable.
The present invention uses a fluid actuated operator for overhead doors of a type which spreads cable sheaves apart to take up cable and lift the door. This enables eliminating springs and counterweights and any other energy storing systems. In a preferred embodiment, a hydraulic actuator is used. Insofar as can be ascertained, no one has heretofore used a hydraulic actuator and cable sheave spreader to open and close overhead doors although hydraulic actuators have been used for other raising and lowering operations for along time. For instance, U.S. Pat. No. 181,761 shows a hydraulic actuator and a cable system for raising and lowering a load-bearing elevator. U.S. Pat. No. 1,188,760 uses a hydraulic actuator to spread apart sheaves over which a cable is run to a load so that when the sheaves are separated from each other by the actuator the load will be lifted. In U.S. Pat. No. 2,943,886 a cable is tensioned with a hydraulic actuator to open the gates on a dump truck. In U.S. Pat. No. 3,823,918 a hydraulic actuator is used to separate sheaves over which a cable is run for moving a scenery bar on a stage. None of these prior patents suggests using a hydraulic actuator on an overhead door, nor does it suggest the type of controls which will be hereinafter described in connection with the new hydraulic actuator, door and control system, combination.